1. Field of the Invention
The present invention relates to an improvement of a plughole waterproofing device for an engine in which a coil case for covering an ignition coil is fitted onto the ignition coil that is accommodated, together with an ignition plug, in a plughole opened to an upper surface of an engine, and in which a longitudinal air path and a vent hole are provided in a case upper portion, protruding above the engine, of the coil case, the longitudinal air path extending upward from a lower end portion of the case upper portion communicating with the plughole, the vent hole communicating with an upper end portion of the longitudinal air path and being opened to ambient air.
2. Description of Related Art
Such a plughole waterproofing device for an engine is already known as disclosed, for example, in Japanese Patent Application Laid-open No. 2008-60188.
In the plughole waterproofing device for an engine disclosed in Japanese Patent Application Laid-open No. 2008-60188 described above, a vent hole is provided in a lower end portion of an upper portion of a case, and a water holding chamber extending upward from an inner end of the vent hole and communicating with an upper end portion of a longitudinal air path is provided in the upper portion of the case. This allows a plughole to breathe as the engine temperature increases or decreases. In addition, the device prevents the plughole from receiving water by holding, in the water holding chamber, water sucked by a pressure decrease in the plughole involved in the decrease of the engine temperature even when the vent hole sinks in a pool formed on an upper surface of the engine. In this regard, the pool may be formed due to: splashed water entering an engine room during driving on a flooded road or a road having a puddle; rainwater entering the engine room during driving on a rainy day; washing water entering the engine room at the time of washing a vehicle; or the like.
In the conventional plughole waterproofing device described above, however, the vent hole is provided in a small size at the lower portion of the water holding chamber. For this reason, when water in the pool drains away, throttle resistance of the vent hole hinders good drainage from the water holding chamber. Accordingly, if the engine repeatedly receives water before water drains away from the water holding chamber completely, the received water enters the vent hole, so that the amount of water in the water holding chamber is increased. If the plughole breathes in such a situation, the plughole might suck water from the water holding chamber.